  /**
     * 字节到MB转换
     * @param size
     * @return
     */
    public static String fileSizeByMB(long size){
        if (size <= 0) {
            return "0";
        }
        final String[] units = new String[]{"B", "kB", "MB", "GB", "TB"};
        int digitGroups = (int) (Math.log10(size) / Math.log10(1024));
        return new DecimalFormat("#,##0.#").format(size / Math.pow(1024, digitGroups)) + " " + units[digitGroups];
    }